Isoparaffinic base oils are useful as engine and industrial oils. There is a significant demand for them because they are superior to conventional base oils due to their better viscosity index, oxidation stability, evaporation losses, low temperature viscosity, metal staining, etc.
Low ring content isoparaffinic base oils are especially desirable because they contain only minor amounts of saturated ring carbon. Saturated ring carbon present in the base oils is detrimental as it lowers viscosity index and alters other characteristics of the base oils so that they are not as useful.
One type of isoparaffinic base oils are PolyAlphaOlefins (PAOs), which are made from the trimerization of 1-decene followed by hydrogenation. However, PAOs are expensive to manufacture because ethylene is used to produce the starting reagent, 1-decene. While PAOs are essentially free of saturated ring carbon as measured by the n-d-M method, PAOs are limited in application due to their cost. Any saturated ring carbon present is primarily naphthenic.
As an alternative route, petroleum-derived wax may be hydroisomerized to produce isoparaffinic base oils. But this process is not ideal because the starting petroleum-derived wax is often more valuable than the resulting isoparaffinic base oil. Furthermore, isoparaffinic base oils produced from petroleum-derived wax contain considerable amounts of saturated ring carbon unless the petroleum-derived wax is first subjected to deoiling, an expensive purification process.
More recently, it has been discovered that Fischer-Tropsch wax can be hydroisomerized to produce isoparaffinic base oils having low ring carbon content. Exploiting the Fischer-Tropsch process is beneficial because various hydrocarbonaceous assets are starting materials for the Fischer-Tropsch process and large quantities of Fischer-Tropsch wax are expected to be available, for example due to (1) conversion of remote natural gas into salable liquid products, (2) conversion of coal into liquid products, and (3) conversion of biomass into liquid products. However, this path to isoparaffinic base oils suffers from certain shortcomings. First, the percentage of wax in Fischer-Tropsch products rarely exceeds 50%; usually the percentage of wax is about 30%. Second, it produces low ring content isoparaffinic base oils with more low molecular weight, low viscosity isoparaffins than high molecular weight, high viscosity isoparaffins. This is due to the molecular weight distribution in Fischer-Tropsch wax, commonly referred to as the Schultz-Flory distribution. According to the Schultz-Flory distribution, the amount of Fischer-Tropsch product with a given carbon number decreases with increasing carbon number (e.g. there are always fewer C10 products than C9 products). Third, hydroisomerization of Fischer-Tropsch wax is not 100% selective and results in a distillate range paraffin by-product. Fourth, the number of Fischer-Tropsch processes might not be able to meet future demand for wax. Fifth, gaining a foothold in the lubricant market with a new base oil composition, such as one produced from Fischer-Tropsch wax, is extremely difficult.
The fit of low ring content isoparaffinic base oils with current products is also problematic. Isoparaffins necessarily impart certain desirable properties to the base oils, for example, high viscosity index and good oxidation stability. However, they can also impart unfavorable characteristics including inadequate additive solubility, inadequate engine deposit solubility, and improper seal shrink/hardening behavior.
Thus, an improved process of producing isoparaffinic base oils is needed. In such an improved process, first, it will be possible to adjust the molecular weight distribution of the isoparaffinic base oil in order to produce both low viscosity and high viscosity base oils. Second, there will be higher (ideally 100%) selectivity for low ring content isoparaffinic base oils rather than by-products, such as distillate range paraffins useful as components in jet and diesel fuel, because the base oils are generally more valuable than the by-products. Third, the starting material for the process will be available in sufficient amounts. Finally, the base oil composition produced by such an improved process will have the desired physical properties and be a composition already sold and well-known on the lubricant market.